It is common for a circuit breakers to employ elements which hip the circuit breakers under various over-current conditions. Such elements, commonly referred to as "hip units," typically respond to relatively long duration overload conditions to trip the breaker when a specified current level is exceeded for a period of time.
When thermal and magnetic elements are employed to trip the circuit breaker, a bi-metallic element responds to relatively long duration overload conditions. In a typical thermal trip unit, at least a portion of the current flowing through the breaker is channelled through the bi-metallic element. The ohmic resistance of the bi-metallic element causes it to generate heat. As the bi-metallic element becomes warmer, it bends and, when it reaches a predetermined temperature, it engages a trip mechanism that releases a latch which holds the breaker contact closed. When this latch is released, the breaker contacts open.
A typical magnetic tripping element includes an armature which is attracted by a magnetic field generated by a relatively high magnitude over-current flowing through the breaker. This magnetic field is concentrated by a magnetically permeable yoke which surrounds the conductor through which the current flows. When the armature is attracted to the yoke, it also engages the trip mechanism causing the circuit breaker to open.
It is desirable to be able to configure and adjust the current levels and current durations, which cause a breaker to trip, beyond the capability of conventional thermal and magnetic trip units. It is also desirable to customize the circuit breaker to a particular application. The use of electronic trip units provides a more accurate adjustment of the current levels. In such electronic trip units, a circuit assembly with switches is used to facilitate such adjustment and configuration by the unit's user.
Although electronic trip units have proven to be beneficial, it has become recognized that the replacement or first-time installation of such electronic trip units in the field requires disassembly of the breaker. First time installation may be required when the user of the breaker desires to upgrade from one trip unit to another. Replacement may become necessary if a component of the electronic trip unit fails. It has also been recognized that different types of electronic trip units cannot be easily interchanged such as when an upgrade is desired or the application so requires.
Accordingly, it is an object of this invention to overcome the disadvantages of conventional electronic trip units.